US2598671A - Frequency distinguishing device - Google Patents

Description

5 Sheets-Sheet 1 |000 FREOUEN GY MG.

FREQUENCY MG Soo Iooo l L. w. BooTHEIY I sso-f--IIH FREQUENCY DISTINGUISHING DEVICE FIRST HARIIIIoNIc oF SIGNAL AT eso Mc SEATING wITH THIRD HARMoNIc oF THE oscILLAToR 3o Mc BELow SIGNAL FREQUENCY o 40o 50o Goo I 3x22o 3o= FIRST HARMoNIG oF SIGNAL AT 69o MG SEATING wITH THIRD HARMoNIG oF THE oScILLAToR 3o Mc ABovE SIGNAL FREQUENCY Ioo 20o soo 4 o soo Goo Too 3xa4o3o June 3, 1952 Filed oct. 1G, 1945 jL IAEGAGYGLE'S oN DIAL June 3, 1952 L. .W. BOOTHBY FREQUENCY DISTINGUISHING DEVICE 5 Sheets-Sheet 2 Filed Oct. 16. 1945 .LEI- E LAWRENCE 'W. BOOTH BY June 3, 1952 l.. ,w. BoTHBY 2,598,671v

FREQUENCY DISTINGUISHING DEVICE Filed oct. 1e, 1945 5 sheets-sheet s LAWREN CE W. BOOTH BY www L. W. BOOTHBY FREQUENCY DISTINGUISHIG DEVICE June 3, 1952 5 Sheets-Sheei' 4 Filed Oct. 16, 1945 Omw mom ...mw mmrohmmhw mZ-J E Ew ...955m mz... o: oom m www mNN N June 3, 1952 L. w. BooTHBY FREQUENCY DISTINGUISHING DEVICE Filed Oct. 16, 1945 5 Sheets-Sheet 5 n OSX o8. oom oom o2 o8 8m o9 oom OOO. Com. OO OO OOw 00m OO 00m mnlhmmmlah Patented June 3, i952 UNITED STATES PATENT OFFICE FREQUENCY DISTINGUI,SIHINGr DEVICE Lawrence W. Boothby, Alexandria', Va. Application October 16, 1945, Serial No. 622,659

s claims. (01.178544) .y (Granted under the act of March 3, 1883, as

one of which-corresponds to the actual carrier frequency being received. l

In the' operation of certain ultra high frequency superheterodyne raido receivers ambiguous frequency 'readings often occur because of the presence of spurious responses. Spurious responses may be produced by non-linearity'in the mixer, and if harmonics of the fundamental frequency lof the local oscillator'combine in the mixer, predominantly with the fundamental of the incoming signal; and to a lesser extent with the higher harmonics of the signal, which are usually of negligible amplitude. Under these circumstances, it is often diiiicult, if not impossible, to determine the true carrier frequency being received.

In the prior art, attempts were made to use one or .more stages of preselection in order to minimize trouble from'spurious responses produced-in superheterodyne receivers. However, prsclection lfor ultra-high frequency receivers which are required to tune over an extended range has not 'proven` feasible to-date. The inductor and capacitor circuit combinations 'commonly employed for wave trap applications atv lower frequencies are unsatisfactory in this instance because of vthe limited tuning ranges which may be obtained, and difficulties due to spurious resonances in the lumped circuits.

Accordingly, it is an object of the present invention to provide simple positive meansfor distinguishing between a plurality of signal -responses, and to thereby enable the selection of a correct frequency reading corresponding tothe fundamental of the carrier frequency actually be-A ing received by the radio receiver.

*A further object of `rthis invention is to provide a frequency distinguishing device having a low insertion loss during the time signals are being received by the superheterodyne receiver.

Still another object of this invention is to provid'za frequency distinguishing device which is simple and compact and which will tune over a frequency range of the order of 26 to 1. n

It is still another object of this invention to provide a frequency distinguishing device which will enable the measurement of frequencies which'are relatively high. Y

Other and further objects of' this invention will be obvious upon understanding of the illustrative embodiments `about to be described, or will be inamended April r30, 1928; 370 O. `G. 757) dicated in the appended claims, and various advantages not referred toherein will occur to one skilled in the art upon 'employment of the invention in practice.

A preferred embodiment of-the invention has been chosen for purposes of illustration and de` scription, and is shown in the accompanying drawings, forming a part of the specification, in which: f

' Fig'. 1 is a diagram illustrating a specific ex-f ampleof the formation of a spurious response;` 2 is a diagram illustrating another specific example of the formation of a spurious'response; Fig. -3 isa diagramV illustrating the formation of spurious responses in general; f Fig.- 4 is a diagram showing, lin a -itypical case, various amplitudes of received spurious responses in relation to the amplitude of the received fundamental frequency; 1 f v 1 Fig. 5 is a schematic diagram of a` system cording to'this invention; l

Fig. 6 is a schematic diagramof a stub connected across a coaxial Aline,.,according to this invention; l I

Fig. '7 is a detailed view of a preferred embodiment of this invention, taken at a T-section which is cut away' in the plane ofV the stub and the coaxial cable to show the switching and frequency adjusting means; Y-

l Fig. 8 is an enlarged detail view of the contact elements'of the device shown in Fig. 'I cut away to show `the conical contact area in the coaxial line; f i

Fig. 9 shows an assembly in plan `view of n a preferred embodiment of this invention;

- Fig. 10 shows a side view ofthe device shown insigne;

Fig. 11 shows various attenuation-curves char' acteristic of the device shown in Figs. 9 and 10," indicating variations in attenuation obtained when the shorting contactor of the device is moved into various positions along the stub at various frequencies and with different lengths of line between the frequency distinguishing device and the superheterodyne receiver;

Fig. 12 shows a typical carrier frequency calibration of a device such as is shown in the Figs. 9 and 10; and

Fig. 13 is a plot of the maximum and minimum attenuation obtainable at various frequencies with a typical device according to this invention.

Referring now to Fig. 1, there is shown diagrammatically the formation of a spurious response in the particular case ofthe first harmonic of the signal at .690 megacycles, beating with the third Ycycles, and the oscillat f nal frequency, to produce laelrvwthesignalharmonic.,V :M -Z From -al'egllsdenatim 'of Ethel yIl-and: lnav-i-ngA afreceivext-whiehtsake according, to Equatieml,

` me dmoftheneeivemsmnc harmonic of thefoscillator, the third harmonic of Y the oscillator b eing 30 megacycles below thelrst harmonic of the signal frequency.

In the particular heterodynereceiver which Figs. lto 4, inclusive tapply, the local oscillator vfrequency fois eigen bythe following:

fWhere fd equals the frequencyzin megacycles'libg indicated on the receiver dialwl1ich.is calibrated.

to correspondfto the frequcncy'of aiitl-re"sonarimec4 fuif-equal?. i

Yof 'the input stage; and in which.' the mtermediate-frequency of, the receiver.

.Y Equation l'st'ates that the secorr'deharmonicof* Y the oscillator frequency, 2fo, tracks below'thedial i Y ffl'quncyfd by a' constant amount equal to the intermediate frequency, f1, of the receivers;AV

In the particular case when fl equals 30 megacycles, Equation 5 becomes:y

signal responses with' reference to the fundamen- K tal signal? 'amplitudeu x arbitrarily taken as Y1,000

When the intermediatf frequency'i's -30 "megathe Y In` mesma exemplaar@ dial l @mfthrieceivenzdian mii-indicare thaw nespunsgeohtaianedl corresponds to" the:Y

Vcantieri frequency'.- only; whem .the osx-.llatorV second harmonic beats with the carrier funda.- menta'lnan the'f secondmarmcnirrof the oscillator is afmeszaryls' `below carriertumdamental mclnsiveivem voften;notthe: seconxlvhannonim'hut melanin@ muren; arnhem. sans.11amarla. etc. may beat with the. mdamentazlzineqnencyofa signalitheneby givin'grvrsmtmsmnous iirecurency Eig.; mhe; on az-fsnunious. response there Vshown is similantm-thexample of Figa 12,1:witlnthecexcepltiorrvthaii .the thiudharf monic of the oscillatoriireqnency;isfinsteazr-l megacycles, ahove.s. the..fundamentalrsignali fre'forjlfrequency tracks below 1 and'isbeatingrwith'. thezfimdamental. 'Sigi-,- Y

' another spurtmsreisponseforithedial: .Y .l Y 4 m 'Figi there. isrdiagrammatically. the general, case: or? the nroduction` 4 et. spul-claus.l :se

. Y Aswzm*sesta*E'Ilaiererisishownthe undamenta'llsigmal frequency` as Well as the seconclharmonie ande theinth harmonieofthe. oscillator beatinggwith l Y thefirsts;condsorgmthharmonicqoffthe-signal Yfxleenienczysz 'Ihe;oscillator :harmonie may; beat Ove. ora l with thesignal harmonic either fl ab talgasv wellY as;v corresponding: additionahspurious y axiali type;pan. adjustable series. yresonant: Wm

' tran coxmzvrisingrV variable inductances amil;capaci` tance elexner-l-ts` t4; andalzfrrespectiwelyygrmseres and; grounded at.. one-:enmraml capahlesd'bein it ispossibleto set down a general relatiomfoe .eww-1e reseensewhich berecevedwer L ,nutrida Equation i. f

. mnceaatmscser f Y 'multiple thereof, from thecentral conduetoreu:

unitsj'Theyaliies of m, Vn, and Ythe plus or Vminus signs of the'ntermediate frequencies in Equation 65am; identieualongsidev eachzcorresponding: re-

spense. The; musicus", responses: obtained, are ape panenblyf nandomlyrdistributedasm that. it is? dime toepredcit which. et" the; sigmalsrreeevyetz responds toi-thee fundamentaksignalifnelencies;

and'y on the basis of a comnanisom cathe: amplimdes .obtained-, a. positive.: identicaiiionaof thefundamental signalgfrequency imma-possible: This: is particularly true; since? the. amplitude. @il ther fundamental canrier,p yfreniienelesfis; .mutageni-1 enallyV lmcvsmr'and' may? khe.varying with.. timzf it Y ethus: ,di-iiicult, to.r distinguish the;

siena-1i frequency'rom agrouposignale cantaim which may vary extremelgrweak signalent considerabeamplitudeag. Y

' AVV'Illia present imentiom resoly'esthea` tionedr dinculties; anda .provides azsfreqiuency:

tinguishing devicewherebyythe i' quency may be:V readily'fselected and;identifiedV f from-amongst';'asgmapffolil spurious. frequenciem which-may: also contain; other rcarrier" undame Vfxteizlluerr'cies belonging' .tol smal frequencies;4 Y "Referring noweto.;

terma: than. input 'line I2 *,-preterahlyi oit/the :me

the., other connected or disconnectedt'asa desired, input'coaxial4 line-'by means of 11Go. The radio receiver:4 lf't, gand; the''indicatorV I8.; a Ycathode?ray tubepare repr gramma-.this gm'ei.; 1

Y Refemingffto Fig.. 6;, thereis;v Y stumm connected across a; coaxial ieeder crm-pnt line 2l to produce allargaattenuation-tomes@- nal. supplied tothe receiver when; the-,ehmting bar 23 lay placed oneehal-fwave length; onintegral.

of the receiver input transmission line-@2te The attenuation of-Athesignal is'dueto the low-f impedance .produced by the eiectof a. snorted haltq Wave stub placed.r acrossaf transmissiorrglina vSuccessive nulle separated by intervals-oil halfen electrical; Waver-length mayalsa be otmd 'alongilsel stubv 20, asv indicated.. The lpositimloft the. nulle, on the `stub L20-fis. independent: of.' pointat which the stubistappec'intothetrim Vvmission line. Y However; the. amount ati-attenua? 'l' tion 1 obtained rat ther V11u-ll. point.- depends;

, 15 whether standing waves on4 thelineprcsent-ga;

Y "l 4, thereis shown a typical Y distribution of the relative Vamplitude Yof spurious Y ingalarge number: of. spurmnsresnonsem: assurdi' Y possibly: additional signalsV from. @there snm esentati: in block die.;` Y

voltage minimum, maximum, or intermediate value at the tapping'point. t

It is possible to calibrate a tuning stu-b over a wide frequency range in terms of the positions of the first null, but a greater accuracy in frequency measurement may be obtained by finding the distance between any two adjacent nulls.

A lumped circuit wave trap utilizing the inductance inherent in a variable condenser may be electrically'equivalent to the stub and amore compact design may be thus obtained in a lower frequency range. However,l this kind of device, unlike the stub, cannot be Vused without special caution', because spurious nulls may be observed when tuning signals higher in frequency than the calibrated range of the lumped circuit.

In any case', however, a switch 25 is provided for switchingthe stub 20 effectively in and out of circuit with the transmission line 2| from the antenna to ythe receiver. 'As above indicated, when the stub is disconnected from the transmission line 2|, the insertion loss due to the wave trap in the antenna lead is negligible, and in this case the signal picked up by the receiver experiences negligible attenuation.

Referring now to Fig. 7, there is shown a coaxial line section 30 having an inner central conductor 3| and an outer conductor 32. A dielectric support 34 for the inner conductor 3| extends a short distance on bothA sides of the axis of the stub 35. The outer conductor 36 of the stub 35 is T-connected to the outer conductor 32 of the coaxial'line 3D. The inner central conductor 31 of the stub 36 is capable of reciprocatory or axial movement lengthwise of the stub. The inner conductor 31 is supported within the stub by the hollowcylinder 38 and, in addition, has its end portion supported by fthe dielectric insert 39. The dielectric insert 39 has interiitting engagement with the dielectric support 374 for the inner conductor 3| and both dielectric members may be comprised, for example, of polystyrene.

In Fig. 8 there is shown an enlarged view of the indented conical contact area 40 forming the electrical connection point or contact area of the inner conductor 3| of the coaxial line Y3|) for connection with the movable vconductor 31 of the stub. The shape of the end of the inner conductor 3'1 of the stub 35 is conical, as indicated at 4|, and is capable of making electrical conta-ct with the similarly shaped indented conical surface 40 formed ofthe inner conductor 3| of the coaxial line 30 when the inner conductor 31 is moved to eifect engagement Vof these surfaces. The surfaces of contact may be plated or formed from solid metals suitable for repeated contactor service, if desired.' By appropriate axial motion of the inner conductor 31 relative to the outer conductor 36, the connection or disconnection of the stub 35 in and out of circuit with the coaxial line 30 is effected. While contact is being made, conductor element 31 of the stub is maintained in pressure contact with the inner conductor 3| at the contact areas 40 and 4|, respectively. The electrical contact may be broken preferably by a sudden retractile action which lcauses the inner conductorl 31 of the stub to be suddenly withdrawn from that of the line 30. Q

From the above description it will be seen that there is thus provided a novel switch for connecting or disconnecting a stub with respect to another coaxial line, the elements of this switch requiring a minimum of space and being of such construction as toenable the shor'ting'contactor, generally designated 42, to be moved along the stub '35 to that minimum distance from 4the co'- laxial line 30 where the stub will be .series-resoi between stub and the coaxial line thus is avoided,

and there results.v an increase in the maximum series-resonant frequency that is obtainable.

If a relatively bulky `switch were employed "between the stub and' coaxial line, it would bediflcult to determine whether the first, second or third nulls were being measured, and, in this case, it also would be necessary to Jmake repeated checks 'along the lengthof the" stub so as tod'etermine the distancebetween adjacent riulls in order to be certain that the length being measured is actually a half wavelength.

In'certain cases, however, where the frequency distinguishing 'device is to be utilized solely in a relatively low frequency range a larger coaxial snap switch may be employed as'shown' in my co"- pendingapplicationf'Ser. No.' 616,937, filed September 17, 1945.' -f l 'I l With the present devi'c'efa direct reading calibration on the'dial is provided and it is unnecessary to check for adjacent nulls thereby increasing thefacility and easeof' operation.

lThe shorting contacter' 42 4comprises the -n- `r gered contact sleeves -44 and 45 which have sliding engagement with the central conductor l31 and theouter conductor 36 of the Astub 35, and serve for short-circuiting these conductors.v` '4 The shorting contacter 42 is capable'of axial motion, generally indicated by the arrows 46, in-

. dependent of the axialmotion of the inner conductor 31. .The anti-resonant frequency of the 'stub 35 may thus be 'adjusted by meanso'f the axial adjustment of the hollow cylinderf38 independently ofthe switch position.' Afteradj-usting the shorting contactor'42 for a definite anti- `resonant frequency, the stub 35 may bedis'connected or connectedto thevcoaxial line 3l!l by the able stub 35, and switching means just-described,

slitted sleeves 41 and 48 are provided (see Figs. 9 and l0) which respectively contact the vinner and outer surfaces of the end of the shorting contactor'42 to the central conductor A31, and to the coaxial stub 35, respectively. The sleeves 41 and 48 each comprise an axially slotted cylinder of spring metal.

Referring further to Figs. 9 'and 10, there is shown a supporting framework 50, a front panel 5I attached to the framework, a switch 52, and a calibrated dial53 mounted on the panel. Mounted at the rear end of the framework 5|l`opposite the control` panel 5| is a U-shaped coaxial line 55 having an input terminal 56 and an output terminal 51. Extending from the switchl'52 is "a relatively long thin rod,58 which slidably fits into the hollow cylindrical sleeve 59I 'which`form`sthe shorting plunger. 'Thehollow cylindrical sleeve 59 has the slit contactor sleeve 41 atits end so'as to make a good electrical contactbetwe'enthe hollow cylindrical sleeve 59 and the central rod. 53 and thus avoid radiation or pickup. lThe stub 35 isT-connected to the bottom of the U-shaped coaxial line 55 While the switch rod 58 passes down the center of the stub 35, thus forming the inner conductor 31 vof the stubcoaxial line, which is shorted to the outer conductor 36 of the'stub 1 coaxial line by means of the contactor fingers 44 and 45 on the hollow cylinder 38, as shown in'Fig.

9 useful with other apparatus such as, for example, in television equipment, radio-locating devices, and many other ultra high frequency applications requiring the use of coaxial switches.

It will be understood, however, that the herein described frequency distinguishing device is not limited in its usefulness to superheterodyne receivers but may be employed for example in connection with untuned receivers as well.

As various other changes may be made in the form, construction and arrangement of the parts herein without departing from the spirit or scope of the invention, and without sacrificing any of its advantages, it is to be understood that all matter herein is to be interpreted as illustrative and not in the limiting sense.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

What is claimed is:

1. In combination, a coaxial line including input and output terminals and a central conductor, a coaxial stub disposed at an angle to said coaxial line and provided with an axially reciprocable central conductor, the central conductor of said line having an indented portion for receiving one end of said axially reciprocable central conductor of said stub, means including a mechanism selectively reciprocating said central conductor axially of said stub into a position of mechanical and electrical contact with said indented portion and out of said position to a point external to the outer conductor of said line to couple said stub into and out of energl7 transferring relationship with said line, a contacter disposed concentrically between the stub central and outer conductors for short circuiting the stub, and a mechanism adjustably positioning said contactor axially of said stub.

2. A frequency distinguishing device comprising a coaxial line having input and output terminals and a central conductor, a coaxial stub disposed at an angle to said coaxial line and including an axially reciprocable central conductor, the central conductor of said line having an indented portion for receiving one end of said axially reciprocable central conductor of said stub, means including a mechanism selectively reciprocating said central conductor of said stub into a position of mechanical and electrical con- 10 tact with said indented portion and out of said position to a point external to the outer conductor of said line to couple said stub into and out of energy transferring relationship with said line, a contactor disposed concentrically between the stub central and outer conductors for short circuiting the stub, and means for selectively positioning said contacter axially in said stub to control the attenuation of a signal of selected frequency in said line.

3. A frequency distinguishing device comprising a coaxial line including an outer conductor and a central conductor, an outer conducting cylinder, said outer conductor of said line provided with an opening, means securing one end of said cylinder to the outer conductor of said line coincident with the periphery of said opening, a reciprocable central conducting rod concentrically mounted in said cylinder, a cylindrical sleeve disposed concentrically between said conducting cylinder and said rod, a shorting contactor mounted on the end of said sleeve nearest said one end of said cylinder for short circuiting said cylinder and said central conducting rod, said sleeve extending axially beyond the other end of said outer conducting cylinder, first flexible contactor means secured to said other end of said cylinder for. electrically short circuiting said cylinder and said sleeve, said central conducting rod extending axially beyond the other end of said sleeve, second flexible contactor means secured to said other end of said sleeve for electrically short circuiting said sleeve and said rod, and means reciprocating said central conducting rod through said opening into and out of contact with a portion of the central conductor of said line.

' LAWRENCE W. BOOTHBY.

REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Number Name Date 2,106,713 Bowen Feb. 1, 1938 2,189,549 Hershberger Feb. 6, 1940 2,245,138 Zottu June 10, 1941 2,373,233 Dow et al. Apr. 10, 1945 2,408,420 Ginzton Oct. 1, 1946 2,499,777 Pound Mar. 7, 1950 2,526,678 Mallett et al. Oct. 24, 1950

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